Utility knives

ABSTRACT

A utility knife comprises a lower elongate part shell 1 and an upper such part shell 3 forwardly fitted with interengaging wedging surfaces whereby they clamp together on relative longitudinal movement. This movement is achieved by turning nut 2 on shank 8 to bear on wall 30. The loosening of the nut 2 to unclamp the part shells and thus permit blade 43 to be pushed forward with slider 42 by pushbutton 41 does not separate the part shells 1 and 3 since the end spur 9 of the shank 8 still rides on arresting web 37. Maximum unscrewing of the nut, however, permits separation e.g. for access to stack of spare blades 60 resiliently held at 59 in the rearward part of shell 1 (now unencumbered by the conventional screw-shank), but does not lead to loss of nut 2 because of a complementary detent configuration 25 at the end of the shank and in the end wall 2a of the nut prevents complete nut/shank separation. Spur 9 can be upwardly sloping at its underside and thus constitute an auxiliary clamping means for part shell 1 against part shell 3.

This invention relates to utility knives.

Utility knives are cutting tools capable of a wide range of usesbasically comprising a handle into which a replaceable knife blade isfitted and immobilised so as to protrude from one end.

In some instances the knife is such that the blades must be completelyremoved and disposed of when the exposed end becomes blunt, at whichtime a new blade is fitted. More commonly, the knife has a blade shapedto possess two sharpened ends (e.g. shaped as a symmetrical trapeziumwith the long edge sharpened) so that when one end becomes blunt theblade can be taken out, reversed, and replaced to expose the other foruse. Only when 19 is other end becomes blunt is the blade completelyreplaced by a new blade. In a preferred form, such blades can also be"retractable" i.e. selectively extendable to any one of a number ofimmobilisable positions.

In recent years the blade has been embodied as a long metal strip,sharpened along one edge and provided with score lines or like lines ofweakness across its width at an acute angle, that is, so as to come to asharp point at the sharpened edge. As for a slmpleretractable blade thiselongated blade is supported within the handle on a carrier, and theresilient part of carrier is biassed against the teeth of a longitudinalrack. A press button extending through a longitudinal slot in the handleenables the user to press the resilient part of the carrier out ofengagement with its rack and slide it up or down within the handle.Thus, the blade can be retracted for safety, or can be forwarded to adesired operative position. When desired, since a line of weakness isapparent, beyond the handle, the blade can be broken transversely toexpose a new sharp point and sharpened edge portion.

Such utility knives often have handles formed essentially as twolongitudinally divided part shells, the exact parting line along thehandle being designed in practice for reasons of function or appearancenot to be a simple straight longitudinal bisection.

Originally, the part shells were held together by one or more transversethreaded bolts. To change, or reverse, a blade the bolts were unscrewed,one shell was removed, and the blade manipulated as necessary. Typicallya "replaceable" blade, whether retractable, and whether for single useor double use is provided with holes or notches to fit by mechanicalinterengagement within the handle so as to resist longitudinal pressure(otherwise serving to push the blade back when in use) and forreplacement the blade has therefore to be removed from and fitted intosuch engagement with corresponding projections or shoulders. Transverseclamping effect on the blade, also serving to grip the blade againstmovement, does exist but is usually of secondary importance against suchlongitudinal movement. It may however be a significant protectionagainst lateral movement of the blade.

More recently, the so-called "wedge-lock" assembly has been used. Inthis, the part shells, at a forward location of their parting line (andon both side regions) are formed with a wedging interlock so directedthat minor longitudinal movement of one part shell relative to the othercauses the wedge formations on the parting line to slide one on theother and thereby draw together, or release, the part shells in atransverse direction. This minor longitudinal movement and thus theclamping or releasing of the part shells can be achieved by a singlebolt with a knurled head for finger operation, located at the rear ofthe handle and threaded in one shell while bearing on the other.

Such a "wedge lock" assembly is particularly useful for the knives withretractable blades. This is because, from time to time, the blade mustbe retracted or must be advanced and then fixed again. The clampingtogether of the two part shells, even if it does not have a major effectin resisting longitudinal pressures in use, does militate against easyadvancement/retraction of the slide over its rack, and it is usuallypreferred to slacken the shells slightly so as to facilitate advancementor retraction. An end bolt and "wedge lock" configuration, manuallyoperated, is much more convenient for this essentially brief adjustmentthan the use of a screwdriver to adjust one or more transverse screws.

In practice it has been established that the transverse blade clampingforce using the "wedge lock" assembly, which is exerted over a wedgingplane, can be a significant component of the longitudinal resistance tomovement of the blade in use; this can lead to advantageousmodifications e.g. in the shape and strength of the rack and slide.

Use of an end, or longitudinal, threaded bolt, instead of a transversebolt or bolts also permits improved design of the effective interior ofthe part shells when assembled. One aspect of this is the readyprovision, even with a short handle, of enough internal space to hold astack of spare blades, of the single or double use type or of theretractable type.

We have now discovered, however, that use of a stationary,rearwardly-projecting, threaded shank with an operating nut threadedthereon, is even more advantageous and permits a number of inter-relateddesign improvements.

In one aspect therefore the invention provides a utility knife of thetype with a handle comprising two elongate part shells capable ofassembly about generally longitudinal parting lines so configured at aforward location thereof that relative longitudinal movement of the partshells may cause them to approach each other and clamp to form anassembly locating and immobilising a blade protruding from one endthereof; in which one part shell is provided with a rearwardly extendingthreaded shank, and the shank passes through an aperture in a rear wallof the other part shell to accommodate a turnable nut whereby relativelongitudinal movement of the part shells may be achieved by turning thenut upon the shank to bear upon said rear wall.

Such a shank can further disencumber the internal space, can give anarrestable member to protect against undesired separation on bladeextension, can give a means of permanently uniting the operating member(i.e. nut) without risk of loss, and can give an auxiliary wedge-face toassist clamping.

Usually the shank is sufficiently long to extend beyond the nut when thepart shells are fully assembled with the nut tightened.

If this is ensured, then a knife can be fabricated in which the saidaperture is an open slot and in which the said other part shell includesa portion located to arrest the shank transversely on such fullassembly. whereby free separation of the part shells cannot be achieveduntil the nut has allowed the first part shell to advance so that theend of the shank is no longer arrested.

For a convenient embodiment we prefer such a knife in which the saidshank terminates in a spur extending rearwardly from part only of theshank cross section; and in which the arrest portion comprises atransverse web located to fit beneath the said spur. For example the webmay be formed to project forwardly from the inner periphery of a ringguard extending from the said other portion rearwardly around the shankand nut. Therefore, if the spur is shaped to have an upwardly slopingundersurface it can be positioned to cooperate with an edge of the saidtransverse web and to constitute a rearwardly located auxiliary clampingconfiguration for the two part shells.

Another additional and alternative configuration is to provide a knifeas defined above in which the shank possesses at least one radialprotuberance at its end and the nut is correspondingly formed with atleast one complementary radial detent formation in an end face, toprevent further rotation and separation of the nut. Preferably the shankpossesses two different radial protuberances successively arranged inthe direction of rotation with (a) a lower gently contoured profile overwhich the detent may resiliently ride in either direction on exertion ofa predetermined and warning level of force and (b) a higher, profilestep-like to prevent further rotation and separation of the nut butgently contoured to permit initial assembly in the other direction.

For convenience in manufacture it is preferred if the two part shellsare integral die cast structures and the thread on the shank isaccordingly interrupted at its sides to permit shell removal from themould.

The invention also extends to use of the space left unencumbered by therearward (i.e. external) protrusion of the shank. Thus the inventionfurther envisages such knives, as described above, accommodating a stackof spare blades at a rearward location of the said first part shell.

Preferably, the stack is held in place by a resilient leaf of materialbiassed downwardly from an elongate holding frame located within thehandle. By way of example a knife may be embodied in which the elongateholding frame defines a longitudinally directed slot with edge portionsdownwardly directed to provide a rigid structure, said slot permittingpassage of the pushbutton of a blade slider protruding from alongitudinal slot in the said other part shell; and in which the frameis foldable upwards about a line forward of the said rigidified edges toallow access to the stack of blades when the part shells are separated.In such an instance a forwardly located position of the said frame maybe downwardly biassed to bear upon the protruding blade.

The invention will be further described with reference to theaccompanying drawings, in which:

FIG. 1 is a median longitudinal section through an embodiment of utilityknife illustrating features of the present invention;

FIG. 2 is a section along line II--II of FIG. 1;

FIG. 3 is a section along line III--III of FIG. 1;

FIG. 4 is a plan view of the lower part of the utility knife shown inFIG. 1 with an assembly nut retracted;

FIGS. 4a, 4b and 4c show details of the assembly nut construction andassembly;

FIG. 5 is a side view of the lower part of the knife as shown in FIG. 4,partly broken away, and with a blade-stack restraint raised;

FIG. 6 is a side view of a variant embodiment of utility knife, partlybroken away; and

FIG. 7 is a side view as in FIG. 6 with the part shells slightly parted.

The utility knife shown in FIGS. 1 to 5 can be considered in three mainparts namely, a lower elongate part shell 1 and associated manuallyoperable assembly nut 2; an upper elongate part shell 3 fitting with thelower shell 1 to define a utility knife handle; and the presentation andstorage assembly 4, located within the assembled part shells 1 and 2with an operative blade end protruding.

The lower elongate part shell 1 can also be seen advantageously in anexternal view in FIG. 5, and in assembly (of a slightly variedembodiment) in the external views of FIG. 6 and 7. It is a die-castalloy structure which externally possesses two forward "wedging"structures 5 (see also FIG. 4) with inclined Wedge surface 6; a smoothbase wall 7; and a rearwardly projecting shank 8 threaded on its upperand lower surfaces and terminating in integral spur 9 extendingrearwardly from its upper portion. Internally it is shaped to supportvarious features of the internal assembly. Thus, forwardly, it possessestwo longitudinal support ribs with coplanar upper edges 11, and twolongitudinal parallel guide walls 12. In an intermediate location itpossesses two further parallel guide ribs 13a, over a thickened wallsection 13b. Rearwardly it possesses two parallel support pillars 14extending from the rear wall 15 of the part shell.

The nut 2 and preferred features of its assembly are shown in FIGS. 4a,4b and 4c. It comprises an integral molded polymer unit with an internalcylinder 16 possessing bore 17 with internal threads 17a and an externalcontoured frustoconical cover 18 spaced from the internal cylinder 16 bylongitudinal ribs 19 and possessing gripping flutes 20 on its outerface. In the end surface thickness 2a of the nut the threaded bore 17 ismodified in shape by means of a recess 21 and a detent 22 adjacentthereto. This nut is assembled on shank 8 with threads 8a, 8b on upperand lower surfaces only (to achieve mold release of the die-castarticle) and may be located inwards of spur 9 as shown in FIG. 1 oroutwards to cover spur 9 as shown in FIGS. 4 and 5.

At the end of spur 9 there is a first integral radial protuberance 23 oflesser radial height and gradual contours 23a and a second suchprotuberance 24 with greater radial height, possessing a step contour 25and a gradual outer slope 25a. These protuberances should be contouredand dimensioned to cooperate with recess 21 and detent 22 as explainedmore fully below.

The upper elongate part shell 3 may again be generally seen from theembodiment of FIGS. 6 and 7. It is again an integral die-cast alloystructure. Externally it possesses two forward wedge structures 26 withwedge surfaces 27, a smooth upper outer wall 28 with an elongate slot 29extending centrally therethrough over a central part of its length, anda downwardly extending rear wall 30. Wall 30 is vertically slotted at31, the slot being open from below to accommodate loosely an internalunthreaded portion 8c of shank 8. The integral structure of the upperpart shell 3 is continued in a protective integral ring wall 32extending behind the nut 2 and the shank 8 and spur 9. The rear,transverse, portion 33 of this ring wall has a integral ledge or web 34extending into the ring space beneath spur 9.

The longitudinal slot 29 of shell 3, as also shown in FIG. 3, hasmutually inclined upper walls 35 and parallel lower walls 37 configuredas teeth 38 to constitute a rack. The end tooth 38a is longer, as a stopmember. The slot 29 also possesses inclined end walls 39.

The shell 3 includes a single integral longitudinally extendingprojection 40 at a rearward position.

The internal assembly 4 comprises an upwardly biassed pushbutton 41 andmetal slider 42, and a trapezoidal blade 43 carried on the slider asknown in the art. The slider 42 is a shallow metal tray and rides uponthe coplanar top edges 11 on walls 10 with its walls 42a located betweenthe internal shell walls 12. It is spring biassed so that it normallyforces the polymer push button 41 upwardly whereby transverseprojections 44 enter between the teeth 38 and are held thereby againstlongitudinal movement. Blade 43 is immobilised on the slider 42 bysuitable lugs or projections in blade recesses 45 opposite cutting edge46.

Above the level of the slider 42 and blade 43 is located an integralleaf of resilient polymeric material 47. This possesses a forwardplatform region 48 (pressed into place between stops 48a in the lowerpart shell 1) and a forwardly projecting resilient central tongue 49possessing shallow ribs 50 on its underside to press against theblade/slider assembly to assist in stabilising it as described below.Rearwardly the leaf 47 has two side portions 51 defining a broad slot 52in which the pushbutton 41 can move without hindrance. The side portions51 have downwardly projecting inner walls 51a defining the edges of theslot 52 and resistant to flexure over a transverse flexing axis. At therearward end a second platform 53 is supported at its rearmost edge 54on the tops of support pillars 14, being held down upon these by theunderside of integral upper part shell projection 40.

Platform 53 defines by downward stepped wall 55 a resilient leaf 59extending along beneath the slot 52 and tapering slightly in width. Atits upper surface the leaf presents a projection 57. This resilient leafholds down a stack of spare blades 60 as shown in FIG. 1 during use ofthe knife.

FIGS. 6 and 7 show an embodiment of the invention which differs indetail. Thus, for example, no stack of spare blades is shown and theinternal structure is unspecified. Many features, however, areidentical, for example the upper part shell 3 and especially itsrearward portions 32, 33 and 34, the shape of the nut 2, and the generalnature of the shank 8 and the spur 9. However, spur 9 differs in detail:instead of extending only from the upper half of the shank 8 it isformed with a slanting lower surface 61 which therefore meets and slidesup the ledge 34 as the nut is tightened. Moreover, projection 40 insideupper part shell 3 is cut away at 62, as shown, to accommodate suchmovement.

Initial assembly of the knife for use, extension or retraction of theblade, and blade replacement, will now be described with reference tothe above illustrated embodiments.

Initial factory assembly starts from lower part shell 1, nut 2, upperpart shell 3, stack of blades 60, slider/pushbutton unit 42/41, theblade 43 and the polymer leaf 47.

Firstly, nut 2 is forced to turn so that the detent 22(a) rides upgently sloping surface 25a and thus over the stepped contour 25 and (b)thereafter rides just past the lesser protuberance 23 with itssymmetrical gentle slopes 23a. At this stage nut 2 will be in therelationship to shank 8 as shown in FIG. 4. Blades 60, slider/pushbutton42/41, and operating blade 43 are then laid in their designated areas,polymer leaf 47 is placed oVer these units. (as a permanent assembledfeature thereafter) and the upper shell is fitted over the wholeassemblage so that the slot 29 passes down over shank portion 8c, sothat the tapering wedge faces 6 and 27 are located opposite one another,and so that the pushbutton 41 extends through the slot in the handle.The nut 2 is tightened, and the two part shells are forced towards oneanother by the action of the wedging surfaces 6 and 27 until the knifeis fully and tightly assembled with the blade held by the slider and bythe two part shells at their forward edges.

For blade advancement and retraction, nut 2 is slackened slightly s thatthe forward edges of the part shells 1, 3 do not grip the blade: slider42 is operated to a new rack position by pushbutton 41: and nut 2 istightened up again. Retraction is of course similar.

For blade replacement from the stack 60, the nut 2 is turned backwardsuntil a transient warning difficulty is encountered by virtue of thedetent 22 riding up and down surfaces 23a, this indicating that the`stop` position then encountered is intentional and that force shouldnot be used to overcome consequent further resistance. The upper halfshell 3 is raised. The leaf 47, being elastic, lifts slightly and can bebent resiliently upwards (see FIG. 5) for easy removal of a blade fromstack 60, and for its use as a replacement of old blade 43. Subsequentreassembly of the components takes place as before.

The structures and operations shown and described demonstrate a numberof advantages over prior art designs.

Firstly, the use of an integral rearwardly projecting shank 8 gives theimmediate advantage, as compared to the use of a through bolt with amanually turnable head, that no space has to be allowed within thehousing, whereby space is available in the unencumbered rearward part ofthe shell for a stack of spare blades.

Also, the joint provision of a spur 9 extending from the upper half ofshank 8, and the integral ledge 34 is a considerable advantage inpractical use. Hitherto, with a threaded bolt, slackening of theassembly for blade advancement or retraction effectively disconnects thetwo shells. The knife assembly can come apart, especially if the user isinexperienced or is working with cold hands or in an awkward location.With the present inventive feature, the two part shells are preventedfrom coming apart completely by the overlap between the spur 9 and theledge 34 until substantially complete turning of the nut, well beyondthat needed for mere advancement or retraction, has taken place. Such aspur can also provide a safety feature for the nut itself. Hitherto,careless unscrewing of the threaded bolt could lead to complete removaland accidental loss. With the present inventive features the nut catchesby detent 22 on protrusion 25 in its rearmost position and thus cannotbe removed and dropped.

The spur moreover can be fashioned as shown in FIGS. 6 and 7, with aslanting undersurface 61. In such a case the spur 9 is not spaced fromledge 34 but rides up over the edge of this ledge. In other words arearwardly located second wedging location is provided, so that the partshells do not clamp first at the front and then progressively alongtheir length but clamp in a controlled fashion essentiallysimultaneously over their whole parting line. This is both better designin that less wear and distortion is likely at the wedging surfaces 6 and27 and convenient to users in that the different available bladethicknesses can both be used in the knife as shown in FIGS. 6 and 7 byway of example.

Finally, the internal location of shank 8, and the facility therebygiven for blade storage can be utilised to give a suitable blade stackretention means of the type shown avoiding rattling of loose blades withunacceptable noise and risk of damage. The nut is retained on spur 9even at maximum possible unturning, so that opening of the handle forblade changeover can be done easily at any time without loss. Also theelongate nature of polymer leaf 47, as possible in the present design,means that the leaf can be given a rigid structure at the sides 51 ofslot 52 where needed as a basis for the stack retaining leaf 59: abendable portion at the platform 48 to allow upward flexure of the leaffor access to the stack; and a resilient tongue 49/50 to keep the sliderand existing blade in place while the stack is being accessed.

I claim:
 1. A utility knife witha handle comprising two elongate partshells which assemble about a longitudinal parting line; forward wedgestructure at said parting line and at a forward location of said handle;means operable to cause one of said part shells to move longitudinallyrelative to the other part shell whereby component parts of said wedgestructure move relatively and cause the said part shells to adoptrelative transverse movement to grip or release a blade in a positionprotruding from a forward end of said handle; said means operable tocause relative longitudinal movement comprising a threaded shankextending rearwardly from one part shell; a rear wall on the other partshell said rear wall being configured to provide an open slot aperturethrough which said shank passes and from which it may be removedtransversely; and a turnable nut on said threaded shank whereby (a)relative longitudinal movement of the part shells may be achieved byturning the nut on the shank to bear upon the said rear wall, and (b)suitable positioning of the nut allows transverse threaded removal.
 2. Autility knife as claimed in claim 1 in which said threaded shank issufficiently long to extend beyond the nut when the part shells arefully assembled with the nut tightened.
 3. A utility knife as claimed inclaim 2 further comprising a transverse arrest portion rearwardlylocated upon the said other part shell to arrest the said threaded shankupon maximum extension with the nut tightened and thereby preventseparation of said part shells bay transverse removal of the threadedshank from the slot aperture until the nut is suitably positioned toallow threaded shank removal.
 4. A utility knife as claimed in claim 3in which said shank terminates in a spur extending rearwardly from partonly of the shank cross section; and in that the arrest portioncomprises a transverse web located to fit beneath the said spur.
 5. Autility knife as claimed in claim 4 in which said other part shellincludes a ring guard extending rearwardly around the shank and nut andsaid web is formed to project forwardly from the inner periphery of saidring guard.
 6. A utility knife as claimed in claim 4 in which said spurhas an upwardly sloping undersurface positioned to cooperate with anedge of the said transverse web and to constitute a rearwardly locatedauxiliary clamping configuration for the two part shells with the nuttightened.
 7. A utility knife as claimed in claim 1 in which saidthreaded shank comprises a radial protuberance at an outer end thereofand in which said nut comprises at least one complementary radial detentat an end face thereof to prevent further rotation and separation of thenut beyond the end of said shank.
 8. A utility knife as claimed in claim7 in which said shank comprises two different radial protuberancessuccessively arranged in the direction of rotation to exhibit (a) alower gently contoured profile over which said detent on said nut mayresiliently ride in either direction on exertion of a predetermined andwarning amount of force and (b) a higher profile which is step-like toprevent further nut rotation but which is also gently contoured topermit initial assembly of the nut on the shank.
 9. A utility knife asclaimed in claim 1 in which each part shell is a unitary die caststructure and in which the threads on said shank are interrupted at sideportions thereof to permit removal from a mold after the die casting.